In general, as means for absorbing vibration generated from a road surface while a vehicle travels, vehicle wheels serve to primarily mitigate vibration, and a suspension system serves to secondarily absorb high vibration that is transmitted through the vehicle wheels, thereby providing occupants with more comfortable riding quality.
An active stabilizer apparatus is provided to minimize sway of the vehicle in left and right directions, which is caused due to vertical road waviness of the road surface and when the vehicle turns left and right while traveling.
In the related art, a stabilizer bar, which is manufactured by using a single member, is mounted to extend in a lateral direction of the vehicle body, and through roll stiffness that the stabilizer bar autonomously has, the stabilizer bar mitigates rolling motion of the vehicle body, which occurs due to a change in relative behavior posture between left and right suspension systems when the vehicle travels, thereby generally stabilizing the posture of the vehicle body.
The stabilizer bar is manufactured through processes of cutting a single round bar or a pipe member to an appropriate length, forming and processing the cut member so that the cut member has a shape and stiffness required for the stabilizer bar, and then performing heat treatment, shot peening, painting, and the like.
However, the stabilizer bar, which is manufactured by using a single member as described above, is a passive stabilizer bar that is easily manufactured at low production costs. However, since the stabilizer bar controls the rolling motion of the vehicle body by using inherent roll stiffness that the stabilizer bar autonomously has, as described above, there is a problem in that it is difficult to effectively inhibit all of the various types of rolling motion that occur when the vehicle travels.
Therefore, recently, an active rotary stabilizer (ARS), which has an actuator to adjust roll stiffness of the stabilizer bar depending on the circumstances, is widely used.
An active rolling stabilizer for a vehicle is configured so that two half-stabilizer bars are coupled at both ends of an actuator, and adjusts roll stiffness of the stabilizer bar by operating the actuator depending on a degree of the rolling motion of the vehicle, thereby stabilizing a posture of the vehicle.
FIG. 1 is a front view of a vehicle body having a stabilizer bar that is manufactured by using a single member, FIGS. 2A to 2C are conceptual views illustrating a process of operating a passive stabilizer for a vehicle according to the related art, FIG. 3 is a schematic view illustrating a state in which an actuator and a stabilizer bar, which are constituent elements of an active rotary stabilizer for a vehicle according to the related art, are connected, FIG. 4 is an exploded perspective view illustrating a torsion damping unit that is a constituent element of the actuator in FIG. 3, and FIG. 5 is a side view illustrating various examples of a shape of an outer circumferential surface of a spline gear formed on an outer circumferential surface of a rotary stabilizer bar.
As illustrated in FIG. 1, a passive stabilizer for a vehicle according to the related art has a stabilizer bar 1 that is manufactured by using a single member and disposed to be elongated in a vehicle width direction toward left and right wheels 20A and 20B at a lower side of a vehicle body. Rolling motion of a vehicle body 10, which occurs when the vehicle turns left and right while traveling, is inhibited by an action of roll stiffness that the stabilizer bar autonomously has.
FIGS. 2A to 2C are conceptual views illustrating a process of operating the passive stabilizer for a vehicle according to the related art, and more specifically, FIG. 2A schematically illustrates a state in which the vehicle travels straight, FIG. 2B schematically illustrates a state in which the vehicle turns right when viewed from the front side, and FIG. 2c schematically illustrates a state in which the vehicle turns left when viewed from the front side.
The stabilizer bar 1 is disposed to be elongated in left and right directions toward the left and right wheels 20A and 20B at the lower side of the vehicle body 10, and coupled to left and right lower arms 21A and 21B by means of stepped bar links 23A and 23B, and the vehicle body 10 is configured to absorb traveling vibration transmitted from the left and right wheels 20A and 20B by means of left and right suspension systems 25A and 25B.
Referring to FIGS. 2A to 2C in more detail, when the vehicle travels straight, the vehicle body 10 does not tilt in any direction, as illustrated in FIG. 2A, such that nearly no roll stiffness is applied by the stabilizer bar 1. When the vehicle turns right, the vehicle body 10 tilts leftward due to inertia, as illustrated in FIG. 2B, and in this case, the stabilizer bar 1 provides, by its own roll stiffness, force to maintain the vehicle body 10 to the right direction. When the vehicle turns left, the vehicle body 10 tilts rightward due to inertia, as illustrated in FIG. 2C, and in this case, the stabilizer bar 1 provides, by its own roll stiffness, force to maintain the vehicle body 10 to the left direction.
As described above, rolling motion of the vehicle body 10 may be controlled to a certain degree by using the stabilizer bar 1 that is manufactured by using a single member, but there is a problem in that it is impossible to cope with various changes in traveling states. Therefore, an active rotary stabilizer 50 for a vehicle has been developed, as described above.
As illustrated in FIG. 3, in the active rotary stabilizer 50 for a vehicle according to the related art, a drive unit 60, which is configured as a motor, is provided at one side in a housing 55, and a reduction unit 70, which reduces rotational force transmitted from the drive unit 60, is provided at the other side in the housing 55.
Here, one stabilizer bar (hereinafter, referred to as “fixed stabilizer bar 80”) of the aforementioned half-stabilizer bars is welded on a drive unit cover 85 that is disposed to support a shaft of the motor while surrounding the housing 55, at the outside of the housing 55 which is adjacent to the drive unit 60. The other stabilizer bar (hereinafter, referred to as “rotary stabilizer bar 90”) is connected to a final output end 71 of the reduction unit 70 in a spline gear connection manner, at the outside of the housing 55 which is adjacent to the reduction unit 70, and receives predetermined rotational force from the drive unit 60 via the reduction unit 70.
Although not illustrated in FIG. 3, in the reduction unit 70, while a sun gear receives rotational force provided from the motor shaft and rotates, a plurality of planet gears around the sun gear is engaged with the sun gear and revolves around the sun gear, and the plurality of planet gears, which revolves around the sun gear, is engaged with a ring gear type housing that surrounds the plurality of planet gears, and serves to reduce rotational force while rotating the ring gear type housing.
The reduction unit 70 having the aforementioned configurations has two sets of sun gears and planet gears which are continuously disposed, thereby forming a reduction ratio to a degree at which rotational force of the drive unit 60 may be uniformly distributed to one side and the other side of the housing 55.
However, in the case of a reduction mechanism using a planetary gear set like an example of the active rotary stabilizer 50 for a vehicle according to the related art, a reduction ratio may be obtained to a certain degree by using the planetary gear set, but there are problems in that this reduction mechanism is not suitable when a higher reduction ratio is required, and a volume thereof needs to be increased in proportion to the required reduction ratio in order to obtain a higher reduction ratio.
That is, even in the case of the aforementioned example of the active rotary stabilizer 50 for a vehicle according to the related art, the planetary gear reduction mechanisms are continuously arranged in two stages to form a required reduction ratio, but the arrangement of the reduction mechanisms in multiple stages greatly degrades efficiency, requires repair and management to devices, and requires separate fixing means for fixing the sun gear and the planet gears, and as a result, there are problems in that it is very inconvenient to fix the sun gear and the planet gears, and the number of working processes is increased as the process of fixing the sun gear and the planet gears is required, and an overall length of an entire product is lengthened, which causes a great deterioration in degree of freedom when designing a complicated lower structure of the vehicle body.
Meanwhile, there is no major problem when rotational force generated by the drive unit 60 is normally transmitted to the fixed stabilizer bar 80 and the rotary stabilizer bar 90 as predetermined torsional force, but impact occurs when reversed torsional force is transmitted to an actuator through the left and right wheels when any one of the left and right wheels passes over an irregular object such as a sinkhole in a road surface or a speed bump while the vehicle is traveling. Therefore, as illustrated in FIG. 4, various types of damping means may be provided in the housing 55 in order to attenuate the impact.
As illustrated in FIG. 4, a damping means 30 in the related art may include a damping housing 31 which has an annular opening and a plurality of receiving ribs 33 that is formed in an annular shape on an inner circumferential surface of the damping housing 31, and shock absorbing pieces 35 which are inserted and positioned between the receiving ribs 33 of the damping housing 31 to absorb impact transmitted from the outside.
However, the active rotary stabilizer for a vehicle according to the related art has a problem in that an overall length of the actuator is increased because the damping means 30 is provided in the housing of the actuator. Essentially, the actuator has a complicated configuration because a predetermined space is at least needed at the lower side of the vehicle body to allow the housing of the actuator to rotate itself, and a mounting unit needs to be provided to guide the rotation of the fixed stabilizer bar and the rotary stabilizer bar, which are connected to left and right sides of the actuator, respectively, and to allow the fixed stabilizer bar and the rotary stabilizer bar to be coupled to the vehicle body. However, the aforementioned increase in overall length of the actuator further complicates a structure of the lower side of the vehicle body in which the actuator is disposed, which leads to a problem that severely damages a degree of design freedom for components.
In addition, in the active rotary stabilizer for a vehicle according to the related art, as illustrated in FIG. 5, the final output end 71 to which the rotary stabilizer bar 90 is connected is provided in the form of an insertion hole 75 outside the ring gear type housing of the reduction unit 70, and the rotary stabilizer bar 90 is inserted into the final output end 71, which is formed in the form of the insertion hole 75, and coupled to the final output end 71 in the spline gear connection manner. A coupling nut 95 is coupled to a tip portion of the final output end 71 from which the rotary stabilizer bar 90 is exposed to the outside of the final output end 71 so as to exert predetermined coupling force in an axial direction of the rotary stabilizer bar 90 inserted into and coupled to the final output end 71, thereby preventing withdrawal of the rotary stabilizer bar 90 and reducing clearance when the spline gears mesh with each other.
However, in the case of the connection manner of the rotary stabilizer bar 90 according to the related art which is configured as described above, since the rotary stabilizer bar 90 is coupled to the reduction unit 70 in the spline gear connection manner, there is a problem in that noise occurs due to a backlash at the moment when rotational force with high torque is transmitted from the drive unit 60 because of clearance between spline gear teeth 73 formed on an inner circumferential surface of the final output end 71 and spline gear teeth 93 formed on an outer circumferential surface of the rotary stabilizer bar 90. This problem is caused because rotational force with high torque generated by the drive unit 60 exceeds coupling force of the coupling nut 95.
As a countermeasure, unlike a case in which a helix angle is applied so that the respective gear teeth 93 are in parallel in a longitudinal direction as illustrated in FIG. 5A, a method of applying a helix angle so that the respective gear teeth 93 has a predetermined inclination angle α in the longitudinal direction as illustrated in FIG. 5B has been proposed, but in the case of applying the helix angle so that the respective gear teeth 93 has a predetermined inclination angle α as illustrated in FIG. 5B, there is a problem in that it is difficult to disassemble the final output end 71 of the reduction unit 70 and the rotary stabilizer bar 90.